Bidirectional imaging with varying intensities

ABSTRACT

A method is provided for forming an image on a media while the media is moved relative to an imaging head. The media can include a pattern of registration sub-regions. The image can include patterns of features, such as color filter features or colored illumination sources which can be registered with the pattern of registration sub-regions. The imaging method can include operating an imaging head to emit a plurality of independently-controllable radiation beams while scanning over media to form an image on the media. The imaging channel of the imaging head can be operated to emit a radiation beam having a first intensity while scanning in a first direction over the media during a first scan and to emit a radiation beam having a second, different intensity while scanning in a second, opposite direction over the media during a second scan.

TECHNICAL FIELD

The invention relates to imaging systems and to methods for formingimages. The invention may be applied to fabricating color filters forelectronic displays, for example.

BACKGROUND

Color filters used in display panels typically include a patterncomprising a plurality of color features. The color features may includepatterns of red, green and/or blue color features, for example. Colorfilters may be made with color features of other colors. The colorfeatures may be arranged in any of various suitable configurations.Prior art stripe configurations have alternating columns of red, greenand blue color features as shown in FIG. 1A.

FIG. 1A shows a portion of a prior art “stripe configuration” colorfilter 10 having a plurality of red (R), green (G) and blue (B) colorfeatures 12, 14 and 16 respectively formed in alternating columns acrossa receiver element 18. Color features 12, 14 and 16 are outlined byportions of a color filter matrix 20 (also referred to as matrix 20).The columns can be imaged in elongated stripes that are subdivided bymatrix cells 34 (also referred to as cells 34) into individual colorfeatures 12, 14 and 16. TFT transistors on the associated LCD panel (notshown) may be masked by areas 22 of matrix 20.

The stripe configuration shown in FIG. 1A illustrates one exampleconfiguration of color filter features. Color filters may have otherconfigurations. Mosaic configurations have the color features thatalternate in both directions (e.g. along columns and rows) such thateach color feature resembles an “island”. Delta configurations(not-shown) have groups of red, green and blue color features arrangedin a triangular relationship to each other. Mosaic and deltaconfigurations are examples of “island” configurations. FIG. 1B shows aportion of a prior art color filter 10 arranged in a mosaicconfiguration in which color features 12, 14 and 16 are arranged incolumns and alternate both across and along the columns.

Other color filter configurations are also known in the art. Whereas theillustrated examples described above show patterns of rectangular shapedcolor filter elements, other patterns including other shaped featuresare also known.

FIG. 1C shows a portion of a prior art color filter 10 with aconfiguration of red (R), green (G) and blue (B) triangular shaped colorfeatures 12A, 14A and 16A. As illustrated in FIG. 1C, each of therespective color features are arranged along columns and are alignedwith matrix 20.

FIG. 1D shows a portion of a prior art color filter 10 with aconfiguration of red (R), green (G) and blue (B) triangular shaped colorfeatures 12A, 14A and 16A. As illustrated in FIG. 1D, each of therespective color features alternate along the columns and rows of colorfilter 10. As shown in FIGS. 1C and 1D, color features 12A, 14A and 16Acan have different orientations within a given row or column.

FIG. 1E shows a portion of a prior art color filter 10 that includes aconfiguration of red (R), green (G) and blue (B) chevron shaped colorfeatures 12B, 14B and 16B. As illustrated in FIG. 1E, each of therespective color features are arranged along columns and are alignedwith matrix 20. Color features 12B, 14B and 16B are formed from stripesthat bend from side to side and are outlined by portions of a colorfilter matrix 20.

FIG. 1F shows a portion of a prior art color filter 10 that includes aconfiguration of red (R), green (G) and blue (B) chevron shaped colorfeatures 12B, 14B and 16B. As illustrated in FIG. 1F, each of therespective color features alternate along the columns and rows of colorfilter 10.

The shape and configuration of a color filter feature can be selected toprovide desired color filter attributes such as a better color mix orenhanced viewing angles.

Various imaging methods are known in the art and can be used to formvarious features on media. For example, laser-induced thermal transferprocesses have been proposed for use in the fabrication of displays, andin particular color filters. In some manufacturing techniques, whenlaser-induced thermal transfer processes are used to produce a colorfilter, a color filter substrate also known as a receiver element isoverlaid with a donor element that is then image-wise exposed toselectively transfer a colorant from the donor element to the receiverelement. Preferred exposure methods use radiation beams such as laserbeams to induce the transfer of the colorant to the receiver element.Diode lasers are particularly preferred for their low cost and smallsize.

Laser induced “thermal transfer” processes include: laser induced “dyetransfer” processes, laser-induced “melt transfer” processes,laser-induced “ablation transfer” processes, and laser-induced “masstransfer” processes. Colorants transferred during laser-induced thermaltransfer processes include suitable dye-based or pigment-basedcompositions. Additional elements such as one or more binders may betransferred.

Some conventional laser imaging systems emit a limited number ofradiation beams. Other conventional systems reduce the time required tocomplete images by controlling hundreds of individually-modulatedimaging channels to emit corresponding radiation beams. Imaging headswith large numbers of such “channels” are available. For example, aSQUAREspot® model thermal imaging head manufactured by Kodak GraphicCommunications Canada Company, British Columbia, Canada has severalhundred independent channels. Each channel can have power in excess of25 mW. An array of imaging channels can be controlled to write a seriesof image swaths which are arranged to form a continuous image.

Radiation beams are scanned along a scan path to form various images. Insome cases, radiation beams are scanned in a first direction during afirst scan and are scanned in a second direction during a second scansuch that the second direction is different than the first direction.Bidirectional imaging refers to the case in which the second directionis opposite to the first direction. Bidirectional imaging techniques canbe used enhance the productivity of the imaging process since the startof each scan need not occur at a common position.

The visual quality of a formed image can be an important considerationin the selection of a particular imaging process. In applications suchas laser-induced thermal transfer of color filter features, the qualityof the formed color filter is dependant on imaging features that havesubstantially the same visual characteristics. For example, oneparticular visual characteristic can include density (e.g. opticaldensity or color density). Density variations among the imaged colorfeatures can lead to objectionable image artifacts. Image artifacts caninclude banding or color variations in imaged features.

Other image artifacts can include the formation of features with roughedges. In U.S. Pat. No. 6,242,140, Kwon et al describe a method formanufacturing a color filter by thermal transfer using a complex laserbeam. Kwon et al. describe that the complex laser beam can be formed ofunit laser beams having different energy distributions. Kwon et al.describe that the complex laser beam can comprise a plurality of unitlaser beams having a high energy intensity at the edges, and a unitlaser beam having a high energy intensity at the center. Kwon et al.describe that such a complex laser beam can be created to increase theslope of the energy distribution at a threshold energy which is theminimum energy transfer, such that the boundary is distinctlytransferred, resulting in a image having excellent edge characteristics.However, this reference does not address the problem of image variationsfrom swath to swath caused by bidirectional scanning.

In U.S. Pat. No. 6,025,860, Rosenfeld et al. describe a digitaldecorating system for transferring a selected image to a surface of anarticle. The system includes a thermal printhead that includes aplurality of energizable heater elements constructed to deliver heat toa thermal line of pixels on a surface of the printhead. Rosenfeld et al.describe that a microcontroller can be used to control various systemsto form a two dimensional image. Rosenfeld et al. describe that thecontroller can classify the pixels corresponding to the image intoperimeter pixels and interior pixels and control energy levels deliveredto produce heat at the perimeter pixels and interior pixels. Rosenfeldet al. describes an edge enhancement technique in which amicrocontroller “looks” for initial transfer pixels and generates higherenergy levels for the pixels that form an edge. The edge pixels arecontrolled to have a higher temperature than the interior pixelscreating a temperature gradient at the edge between heated and unheatedregions. Rosenfeld et al. describe that the temperature gradient enablesthe transferred material to separate form the material remaining on thefoil in a well defined manner. Rosenfeld et al. also describe a “linesmoothing” routine that eliminates a stair-step appearance of lines oredges that lie diagonally to the direction of thermal transfer motion.Rosenfeld et al. describe that a low level of energy is applied to apixel lying outwardly of an edge pixel (i.e., a pixel not assigned aspart of the computer generated image). Rosenfeld et al. describe that adecreased thermal gradient is produced at the edges which produces lessprecisely defined lines that effectively smooth the line that wouldotherwise have a stair step appearance. While this reference addressesthe smoothing of edges, it does not address the problem of imagevariations from swath to swath caused by bidirectional scanning.

In U.S. Pat. No. 5,321,426, Baek et al. describe a printhead arrangementwhich includes two outboard “dummy” channels. The printhead is used in athermal dye transfer process. The dummy channels produce dummy scanlines which are not used for actual writing, but rather for preheatingand postheating inner scan lines to help alleviate banding. Baek et al.describe that the dummy channels can be operated to write at a constantlaser power level near the threshold point of dye transfer to helpreduce density variations between swaths. However, it does not provide asolution to the problem of image variations from swath to swath causedby bidirectional scanning.

Artifacts such as banding can be difficult to correct and typicallyrequire the establishment of imaging parameters that lead to formationof adjacent swaths that include substantially the same characteristics.It has been noted however by the present inventors that when the sameimaging parameters are employed to scan radiation beams both in a firstdirection during a first scan and a second direction different from thefirst direction during a second scan, various image artifacts can stillarise. This can impact the usefulness of imaging methods such asbidirectional imaging.

There remains a need for effective and practical imaging methods andsystems that permit making high-quality images of features whilescanning in multiple scan directions.

There remains a need for effective and practical imaging methods andsystems that permit making high-quality images of features in abidirectional imaging system.

There remains a need for imaging methods that can be used to reducedifferences between portions of an image formed by radiation beamsscanned in a first direction during a first scan and additional portionsof the image formed by radiation beams scanned in a second directionopposite to the first direction during a second scan.

There remains a need for improved imaging methods that can form aplurality of features with substantially the same characteristics whilescanning in opposite scan directions.

SUMMARY OF THE INVENTION

The present invention relates to a method for forming an image on amedia while the media is moved relative to an imaging head. The mediacan include a pattern of registration sub-regions, such as, for example,a matrix. The image can include one or more patterns of features, suchas color features for a color filter or colored illumination sources aspart of an organic light emitting diode display. The one or morepatterns of features can be registered with the pattern of registrationsub-regions. The features could be island features where each feature ofa first plurality of features of a first color is separated from eachother feature of the first color by a feature of a different color. Thefeatures can be stripes which may or may not be interrupted in one ormore directions. The edges of the features can be skewed with respect toan arrangement direction of the imaging channels.

The images can be formed by a laser-induced thermal transfer processsuch as a laser-induced dye-transfer process, a laser induced masstransfer process or by other means of transferring a material from adonor element to a receiver element.

The imaging method can include operating an imaging head to emit aplurality of independently-controllable radiation beams while scanningover media to form an image on the media. Each channel is capable ofemitting radiation beams. A radiation beam is emitted every time thechannel is turned on. Thus, as a channel is turned on and off, each timethe channel is turned on, a new radiation beam is emitted from thatchannel.

An imaging channel of the imaging head can be operated to emit aradiation beam having a first intensity while scanning in a firstdirection over the media during a first scan and to emit a radiationbeam having a second intensity while scanning in a second direction overthe media during a second scan. The second direction is opposite to thefirst direction and the second intensity is different from the firstintensity. A third radiation beam having a third intensity can form athird pixel. This radiation beam can have an intensity greater than thefirst and second intensities.

A first pixel can be formed with the radiation beam having the firstintensity during the first scan, and a second pixel can be formed withthe radiation beam having the second intensity during the second scan.The first and second pixels can be formed with different exposures. Thefirst intensity can be greater or less than the second intensity. Theradiation beam having the first intensity can form an exposure that isdifferent than the exposure formed by the radiation beam having thesecond intensity. Either one or both of these exposures can be above orbelow the exposure threshold of the media and can be greater than theexposure which occurs due to the leakage intensity when the imagingchannel is operated to not emit a radiation beam.

The imaging head can include a light valve and a channel of the lightvalve can be attenuated to make the second intensity different from thefirst intensity. In another embodiment, the light valve channel can bepulse width modulated to make the second intensity different from thefirst intensity. In yet another embodiment, the power provided to theimaging channel can be varied to make the second intensity differentfrom the first intensity. These methods of varying the intensity can becombined and used simultaneously.

The first pixel can form a part of an edge portion or an interiorportion of a feature. Similarly, the second pixel can form part of anedge portion or an interior portion of the feature or an additionalfeature. An edge portion can extend in a direction which intersects thescan direction or can extend in a direction which is parallel to thescan direction. In one embodiment, the imaging method includes operatingan imaging channel of an imaging head to emit a plurality of radiationbeams while scanning over media. Intensity information associated withthe imaging channel is maintained which specifies a first intensity toset for a radiation beam in the event that the radiation beam is emittedwhile scanning over the media in a first direction, and specifying asecond intensity that is different from the first intensity to set forthe radiation beam in the event that the radiation beam is emitted whilescanning over the media in a second, opposite direction. The directionof the scan is determined and the imaging channel is controlledaccording to the intensity information to emit the radiation beam withthe intensity corresponding to the determined direction.

In one embodiment, the intensity information specifies the firstintensity in the event that the radiation beam is required to form afirst pixel on the media while scanning in the first direction, andspecifies the second intensity in the event that the radiation beam isrequired to form a second pixel on the media while scanning in thesecond direction. The method includes determining if the first pixel isto be formed on the media while scanning in the first direction anddetermining if the second pixel is to be formed on the media whilescanning in the second direction. The imaging channel is controlled toemit the radiation beam to form either the first pixel or the secondpixel.

The intensity information can specify the first intensity in the eventthat the first pixel is an edge pixel, and can specify the secondintensity in the event that the second pixel is an edge pixel. Themethod can include determining if either, or both, of the first pixeland the second pixel are edge pixels. The pixels can be formed withexposures which are different from one another. Each of the intensitiescan be less than or greater than a level sufficient to create anexposure greater than or equal to an exposure threshold of the media.

In one embodiment, an imaging channel of an imaging head is operated toemit a plurality of radiation beams while scanning over media. Firstintensity information associated with the imaging channel is maintained.The first intensity information specifies a first intensity to set for afirst radiation beam in the event that the first radiation beam isscanned over the media in a first direction. Second intensityinformation associated with the imaging channel is maintained. Thesecond intensity information specifies a second intensity different fromthe first intensity to set for a second radiation beam in the event thatthe second radiation beam scanned over the media in a second directionopposite to the first direction. A determination is made when the firstradiation beam is to be scanned in the first direction and the intensityof the first radiation beam is set according to the first intensityinformation. A determination is made when the second radiation beam isto be scanned in the second direction and the intensity of the secondradiation beam is set according to the second intensity information.

In another embodiment, an imaging method can include operating animaging head to emit a plurality of independently-controllable radiationbeams while bidirectionally scanning over media to form an image on themedia. While scanning over the media during a first scan, an imagingchannel of the imaging head can be controlled to emit a radiation beamhaving a first intensity, the first intensity corresponding to anintensity value selected from a first set of two or more intensityvalues. While scanning over the media during a second scan, the imagingchannel of the imaging head can be controlled to emit a radiation beamhaving a second intensity, the second intensity corresponding to anintensity value selected from a second set of two or more intensityvalues. At least one intensity value of the first set is different fromat least one intensity value of the second set. One or more pixels canbe formed with at least one of the radiation beams having the firstintensity and one or more pixels can be formed with the radiation beamhaving the second intensity.

In one embodiment, a plurality of pixels is formed during the firstscan. A first pixel of the plurality of pixels is formed by operatingthe imaging channel to emit the radiation beam having the firstintensity and a second pixel of the plurality of pixels is formed byoperating the imaging channel to emit a radiation beam with a thirdintensity. The third intensity corresponds to an additional intensityvalue selected from the first set. The first set may or may not includeat least one intensity value corresponding to a below-thresholdintensity. The method may include determining if the first pixelcorresponds to an edge portion of a feature formed on the media and thefirst intensity may be boosted for this edge portion.

A program product can be used to carry out the various embodiments ofthe invention. For example, a program product carrying a set ofcomputer-readable signals can be used which includes instructions which,when executed by a controller, cause the controller to operate animaging head to emit a plurality of independently-controllable radiationbeams while scanning over media to form an image on the media. Theprogram product can operate an imaging channel of the imaging head toemit a radiation beam having a first intensity while scanning in a firstdirection over the media during a first scan. The program product canoperate the imaging channel to emit a radiation beam having a secondintensity while scanning in a second direction over the media during asecond scan. The second direction is opposite to the first direction andthe second intensity is different from the first intensity.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments and applications of the invention are illustrated by theattached non-limiting drawings. The attached drawings are for purposesof illustrating the concepts of the invention and may not be to scale.

FIG. 1A is a plan view of a portion of a prior art color filter;

FIG. 1B is a plan view of a portion of another prior art color filter;

FIG. 1C is a plan view of a portion of a prior art filter includingtriangular shaped features;

FIG. 1D is a plan view of a portion of another prior art filterincluding triangular shaped features;

FIG. 1E is a plan view of a portion of a prior art filter includingchevron shaped features;

FIG. 1F is a plan view of a portion of another prior art filterincluding chevron shaped features;

FIG. 2 is a schematic representation of a multi-channel headconventionally imaging a pattern of features onto imagable media duringa plurality of scans;

FIG. 3 is a schematic perspective view of the optical system of anexample prior art multi-channel imaging head;

FIG. 4A is a is a schematic view of apparatus forming a first portion ofan image during a first scan as per an example embodiment of theinvention;

FIG. 4B is a is a schematic view of the apparatus of FIG. 4A forming asecond portion of the image during a second scan;

FIG. 5 is flow chart representing a method practiced as per an exampleembodiment of the invention;

FIG. 6 is a schematic block diagram illustrating a logic used by a lightvalve driver system as per an example embodiment of the invention;

FIG. 7 is a schematic block diagram illustrating a logic used by a lightvalve driver system as per an example embodiment of the invention: and

FIG. 8 shows a photograph comparing a media scanned bidirectionally andunidirectionally

DETAILED DESCRIPTION

Throughout the following description specific details are presented toprovide a more thorough understanding to persons skilled in the art.However, well-known elements may not have been shown or described indetail to avoid unnecessarily obscuring the disclosure. Accordingly, thedescription and drawings are to be regarded in an illustrative, ratherthan a restrictive, sense.

FIG. 2 shows a conventional laser-induced thermal transfer process beingused to fabricate a color filter 10. An imaging head 26 is provided totransfer image-forming material (not shown) from a donor element 24 toan underlying receiver element 18. Donor element 24 is shown as beingsmaller than receiver element 18 for the purposes of clarity only. Donorelement 24 may overlap one or more portions of receiver element 18 asmay be required. Imaging head 26 can include one or more imagingchannels. In this case, imaging head includes an arrangement (i.e.channel array 43) of individually addressable channels 40.

Receiver element 18 can include a registration region with which it isdesired to form images of one or more features in substantial alignment.Receiver element 18 can include a pattern of registration sub-regionswith which it is desired to form images of one or more features insubstantial alignment. In this case, receiver element 18 includes aregistration region 47 (schematically represented in large brokenlines). In this case, registration region 47 includes a color filtermatrix 20. Matrix 20 is an example of a pattern of registrationsub-regions. Although a laser-induced thermal transfer process could beused to form matrix 20 on receiver element 18, matrix 20 is typicallyformed by lithographic techniques.

Donor element 24 includes an image-forming material (not shown) that canbe image-wise transferred onto the receiver element 18 when radiationbeams emitted by imaging head 26 are scanned across donor element 24.Red, green and blue portions of filter 10 are typically imaged inseparate imaging steps; each imaging step involving replacing thepreceding color donor element with the next color donor element to beimaged. Each of the red, green and blue features of the filter istypically transferred to receiver element 18 in substantial alignmentwith a corresponding matrix cell 34. After the color features have beentransferred, the imaged color filter may be subjected to one or moreadditional process steps, such as an annealing step, for example, tochange one or more physical properties (e.g. hardness) of the imagedcolor features.

An example of an illumination system employed by a conventionallaser-based multi-channel imaging process is schematically shown in FIG.3. A spatial light modulator or light valve is used to create aplurality of imaging channels. In the illustrated example, linear lightvalve array 100 includes a plurality of deformable mirror elements 101fabricated on a semi-conductor substrate 102. Mirror elements 101 areindividually addressable. Mirror elements 101 can bemicro-electro-mechanical (MEMS) elements, such as deformable mirrormicro-elements, for example. A laser 104 can generate an illuminationline 106 on light valve 100 using an anamorphic beam expander comprisingcylindrical lenses 108 and 110. Illumination line 106 is laterallyspread across the plurality of elements 101 so that each of the mirrorelements 101 is illuminated by a portion of illumination line 106. U.S.Pat. No. 5,517,359 to Gelbart describes a method for forming anillumination line.

A lens 112 typically focuses laser illumination through an aperture 114in an aperture stop 116 when elements 101 are in their un-actuatedstate. Light from actuated elements is blocked by aperture stop 116. Alens 118 images light valve 100 to form a plurality of individualimage-wise modulated beams 120, which can be scanned over the area of asubstrate to form an imaged swath. Each of the beams is controlled byone of the elements 101. Each element 101 corresponds to an imagingchannel of a multi-channel imaging head.

Each of the beams is operable for imaging, or not imaging, an “imagepixel” on the imaged receiver element in accordance with the drivenstate of the corresponding element 101. That is, when required to imagea pixel in accordance with the image data, a given element 101 is drivento produce a corresponding radiation beam with an intensity magnitudeand duration suitable for forming a pixel image on the substrate. Whenrequired not to image a pixel in accordance with the image data, a givenelement 101 is driven to not produce a radiation beam. As used herein,pixel refers to a single element of image on the substrate, asdistinguished from the usage of the word pixel in connection with aportion of an image displayed on an assembled display device. Forexample, if the present invention is used to create a filter for a colordisplay, the pixels created by the present invention will be combinedwith adjacent pixels, to form a single pixel (also referred to as afeature) of an image displayed on the display device.

FIG. 2 shows a portion of a color filter receiver element 18 that hasbeen conventionally patterned with a plurality of red stripe features30A and 30B in a laser-induced thermal transfer process. FIG. 2 depictsthe correspondence between imaging channels 40 and the transferredpattern as broken lines 41. Features, such as stripes 30A and 30Bgenerally have sizes that are greater than a width of a pixel imaged byan imaging channel 40. The radiation beams generated by imaging head 26are scanned over receiver element 18 while being image-wise modulatedaccording to image data specifying the pattern of features to bewritten. Groups 48 of channels 40 are driven to produce radiation beamswherever it is desired to form a feature. Channels 40 not correspondingto the features are controlled so as not to image corresponding areas.

Receiver element 18, imaging head 26, or a combination of both, aremoved relative to one another while imaging channels 40 are controlledin response to image data to create image swaths. In some cases, imaginghead 26 is stationary and receiver element 18 is moved. In other cases,receiver element 18 is stationary and imaging head 26 is moved. In stillother cases, both the imaging head 26 and the receiver element 18 aremoved.

Imaging channels 40 can be activated to form an image swath during ascan of imaging head 26. Receiver element 18 can be too large to beimaged within a single image swath. Multiple scans of imaging head 26are typically required to complete an image on receiver element 18.

Movement of imaging head 26 along sub-scan axis 44 may occur after theimaging of each swath is completed along main-scan axis 42.Alternatively, with a drum-type imager, it may be possible to relativelymove imaging head 26 along both the main-scan axis 42 and sub-scan axis44, thus writing the image with swaths extending helically on the drum.In FIG. 2, relative motion between imaging head 26 and receiver element18 is provided along a path aligned with main-scan axis 42. In thiscase, receiver element 18 is movable in a forward direction 42A and in areverse direction 42B with respect to imaging head 26. Forward direction42A is opposite to reverse direction 4213. Receiver element 18 canreciprocate between forward direction 42A and reverse direction 42B. InFIG. 2, relative motion between imaging head 26 and receiver element 18is provided along a path aligned with sub-scan axis 44. In this case,imaging head 26A can move in an away direction 44A and in a homedirection 44B. Away direction 44A is opposite to home direction 44B.

Any suitable mechanism may be applied to move imaging head 26 relativeto receiver element 18. Flat bed imagers are typically used for imagingreceiver elements 18 that are relatively rigid, as is common infabricating display panels. A flat bed imager has a support that securesa receiver element 18 in a flat orientation. U.S. Pat. No. 6,957,773 toGelbart describes a high-speed flatbed imager suitable for display panelimaging. Alternatively, flexible receiver elements 18 can be secured toeither an external or internal surface of a “drum-type” support toaffect the imaging of the image swaths.

In FIG. 2, stripe features 30A are imaged during a first scan in whichimaging head 26 (in first position 38A) directs radiation beams towardsreceiver element 18 as receiver element 18 is moved in reverse direction42B. On completion of the first scan, imaging head 26 (in first position38A) is moved along sub-scan axis 44 to a second position 38B (shown inbroken lines). Stripe features 30B are imaged during a second scan inwhich imaging head 26 (in new position 38B) directs radiation beamstowards receiver element 18 as receiver element is moved in forwarddirection 42A. Stripe features 30A and 30B are imaged by bidirectionalscanning techniques. Bidirectional scanning techniques can enhanceimaging productivity since scans are made on both in a forward scanningdirection and a reverse scanning direction.

Banding typically refers to an image artifact that repeats in adirection that intersects a direction in which the image swaths extend.Some banding artifacts are typically characterized by visual differencesthat repeat from image swath-to-image swath. For example, if adjacentimage swaths are separated from one another by a gap, the gaps canrepeat to produce a banding artifact. If adjacent image swaths overlapeach other, the overlapped regions can repeat to produce a bandingartifact. If density variations occur across each of the image swaths ina repeatable manner, the repeating density variations can produce abanding artifact. Banding artifacts can arise from image variations inareas proximate to image swath-to-image swath boundaries. Bandingartifacts can arise from variations within an image swath that repeatfrom image swath-to-image swath. Many banding artifacts repeat onintervals related to the image swath width.

The present inventors have surprisingly noted that other image artifactscan arise when bidirectional imaging techniques are employed. Visualdifferences have been noted when a first image swath formed by scanningin a first direction is compared against a second image swath formed byscanning in a second direction that is opposite to the first direction.When many image swaths are formed using bidirectional scanningtechniques in which image swaths imaged in the first direction alternatewith image swaths imaged in the second direction, the visibledifferences between the adjacent swaths repeat to produce a“banding-like” artifact. In this case, the differences repeat every twoswath widths when two image swaths formed by scanning in the firstdirection are separated from one another by a third image swath formedby scanning in the second direction. Visible differences can includedifferences in density (e.g. optical density or color density).

Referring back to FIG. 2, visible differences can arise between stripefeatures 30A and 30B even though they are substantially identical inshape and size. Visible differences can occur even when a given stripe30B is imaged during the second scan by the same group 48 of imagingchannels used to image a given stripe 30A during the first scan. In thiscase, the bidirectional nature of the scans imparts visible differencesbetween their associated imaged features.

FIG. 8 is a photograph comparing a series of image swaths imaged usingconventional bidirectional and unidirectional techniques. Image 51A isimaged unidirectionally with a plurality of image swaths 55, each ofwhich was scanned along a common direction. Image 51B is imagedbidirectionally with a plurality of image swaths 57A and 57 B. Imageswaths 57A were scanned along a direction that is opposite to thedirection in which image swaths 57B were scanned. Both images 51A and51B were formed by laser-induced thermal transfer. Although some minorswath-to-swath banding was present (not clearly visible in thisphotograph), image 51A shows that each of image swaths 55 have similarvisual characteristics. In comparison, image 51B clearly shows visualdifferences between the bidirectionally imaged swaths 57A and 57B. Abanding artifact that repeats every two swaths is visible. Although thisartifact is clearly visible with the unaided eye, the FIG. 7 photographhas been enhanced for reproduction herein.

Although they do not want to be by any particular theory, the presentinventors consider that one or more various causes can contribute tovisual differences between the various image portions formed bybidirectional scans. Without limitation, one possible cause may includeinteraction effects between the radiation beams and the media itself.For example, in various laser induced thermal transfer processes,radiation beams are scanned across the media assemblage to cause animage forming material to separate from a donor element and betransferred to a receiver element. Various characteristics that aredependant on a particular direction of the scan may be developed withinthe transferred image forming material. For example, the shape of atransferred pixel of the image forming material may be dependant on thedirection of the scan. The distribution of the transferred imagedforming material may also change in each direction. Optical propertiessuch as reflectivity may vary as a function of direction.

Exposure, E is defined in optics as the integral of intensity over time.Many imagable media respond to exposure. Exposure is related to anintensity of a radiation beam and exposure time of the radiation beam.Exposure can be related to the scanning speed of the radiation beam.Some imagable media follow the “law of reciprocity”. For example, amedia that follows the law of reciprocity can be exposed by radiationintensity I for a duration t, or with radiation intensity 10I for aduration 0.1t with similar results. In either case, the exposure is thesame (i.e. 10I×0.1t=I×t). Some media comprising photo-resists orelectron beam resists are examples of media that behave substantially inaccordance with the reciprocity law. There are other imagable media thatdo not obey the reciprocity law. Media that do not obey the reciprocitylaw include some thermal imaging materials. In some media, an image isformed when an exposure created by a radiation beam reaches, or exceedsan exposure threshold level associated with the media. In some media,the exposure threshold depends on the intensity. In some media, aminimum intensity threshold must be equaled or exceeded in order to forman image. In some cases, a media may behave substantially in accordancewith the reciprocity law over a limited intensity range.

FIGS. 4A and 4B schematically show an apparatus 80 used in an exampleembodiment of the invention. Apparatus 80 is operable for forming imageson receiver element 18. In this example embodiment of the invention,images are formed on receiver element 18 by operating imaging head 26 todirect radiation beams while scanning over receiver element 18. Theoperation of apparatus 80 during a first scan is shown in FIG. 4A andthe operation of apparatus 80 during a second scan is shown in FIG. 4B.

Apparatus 80 includes carrier 52 which is operable for conveyingreceiver element 18 along a path aligned with main-scan axis 42. Carrier52 can move in a reciprocating fashion. In this example embodiment ofthe invention, carrier is movable in a forward direction 42A and areverse direction 42B. Imaging head 26 is arranged on a support 53 thatstraddles carrier 52. Imaging head 26 is controlled to move along pathsaligned with sub-scan axis 44. In this example embodiment of theinvention imaging head 26 can be controlled to move along support 53.Imaging head 26 is movable in away direction 44A and in home direction44B. Apparatus 80 forms images by bi-directionally scanning receiverelement 18.

In this example embodiment of the invention, a laser induced thermaltransfer process is employed. Imaging head 26 is controlled to scan themedia with a plurality of radiation beams to cause an image formingmaterial (not shown) to be transferred from donor element 24 to receiverelement 18. Imaging electronics (not shown) control activation timing ofthe imaging channels 40 to regulate the emission of the radiation beams.Motion system 59 (which can include one or more motion systems) includesany suitable prime movers, transmission members, and/or guide members tocause the motion of carrier 52. In this example embodiment of theinvention, motion system 59 controls the motion of imaging head 26 andcontrols the motion of carrier 52. Those skilled in the related art willrealize that separate motion systems can also be used to operatedifferent systems within apparatus 80.

Controller 60, which can include one or more controllers, is used tocontrol one or more systems of apparatus 50 including, but not limitedto, various motion systems 59 used by carrier 52 and imaging head 26.Controller 60 can also control media handling mechanisms that caninitiate the loading and/or unloading of receiver element 18 and donorelement 24. Controller 60 can also provide image data 240 to imaginghead 26 and control imaging head 26 to emit radiation beams inaccordance with this data. Various systems can be controlled usingvarious control signals and/or by implementing various methods.Controller 60 can be configured to execute suitable software and caninclude one or more data processors, together with suitable hardware,including by way of non-limiting example: accessible memory, logiccircuitry, drivers, amplifiers, A/D and D/A converters, input/outputports and the like. Controller 60 can comprise, without limitation, amicroprocessor, a computer-on-a-chip, the CPU of a computer or any othersuitable microcontroller.

The present invention provides systems and methods in which an intensityof the radiation beams produced by imaging head 26 are adjusted in waysthat reduce image artifacts when bi-directional scanning techniques areemployed. FIG. 5 shows a flow chart for imaging a pattern of featuressuch as stripe features 30C and 30D shown in FIGS. 4A and 4B as per anexample embodiment of the invention. Stripe features 30C and 30D aresimilar to stripe features 30A and 30B shown in FIG. 2 and arecollectively referred to as stripe features 30. The pattern of featuresis formed by a plurality of scans. The following description of the FIG.5 flow chart refers to apparatus 80 as schematically shown in FIGS. 4Aand 4B, although it is understood that other apparatus are suitable foruse with the illustrated process. The process begins at step 300 whereimaging head 26 forms a first portion 71 of the image on receiverelement 18. In this example embodiment of the invention, the first imageportion 71 includes stripe features 30C. Controller 60 controls imaginghead 26 to direct radiation beams along a first scan path to form firstimage portion 71 on receiver element 18.

As schematically shown in FIG. 4A, first image portion 71 is formedduring a first scan in which imaging head 26 is operated to scan groupsof radiation beams in a first scan direction. In this exampleembodiment, each stripe feature 30C is imaged by a plurality ofradiation beams during a first scan. During the first scan, controller60 controls motion system 59 to move carrier 52 along a first path. Inthis example, carrier 52 is moved in reverse direction 42B. In thisexample embodiment of the invention, carrier 52 can accelerate from astarting speed (which can include a zero velocity) to a speed suitablefor scanning. In this example embodiment of the invention, the speed isheld constant as imaging head 26 directs radiation beams to form firstimage portion 71.

Stripe features 30C in first image portion 71 are formed in accordancewith image data 240 corresponding to image portion 71. Image data 240can include raster data. Controller 60 controls the activation ofradiation beams emitted from imaging head 26 in accordance with imagedata 240. In this example embodiment, imaging head 26 has a plurality ofimaging channels 40 and each stripe feature 30C is imaged by a group 48of imaging channels 40. In this example embodiment, each group 48 ismade up of approximately five contiguous imaging channels 40. An imagingchannel 40 can be turned “on” emit a radiation beam. Each time theimaging channel is turned on, it emits a radiation beam. In this case, aradiation beam can be used to transfer material from donor element 24 toreceiver element 18 along a scan line corresponding to the channel.Channels (i.e. such as imaging channel 45) in groups 48 are turned “on”.An imaging channel 40 may also be turned “off” so that a radiation beamis not emitted. The intensity of each beam is controllable from aninactive intensity level in which the imaging channel is turned “off” toan active intensity level in which the channel is turned “on”. Theinactive intensity level can include an intensity level equal to zero orsome small intensity level representative of various leakage effects.Some example embodiments of this invention (e.g. those employingindependently modulated laser sources) have inactive intensity levelsequal to zero.

The active intensity level of the imaging beam is also adjustable andsome material may be transferred between donor element 24 and receiverelement 18 across a range of intensity levels. Adjustment of intensitycan include, for example, modulating the intensity of the beam.Adjustment of intensity can include, for example, attenuating theintensity of the beam. Adjustment of intensity can include, for example,adjusting a power of the beam. Controller 60 controls imaging channels40 selected to emit radiation beams with intensities suitable forforming imaged pixels base on several factors. For example, inaccordance with image data 240, imaging channel 45 emits a radiationbeam (not shown) suitable for forming an image pixel that forms a partof one of the stripe features 30A. The intensity of the radiation beamwill be based in part on the properties of the media that is to beimaged. In some example embodiments of the invention, the intensity ofthe radiation beam emitted by imaging channel 45 is controlled to equalor exceed an exposure threshold associated with the media. In someexample embodiments of the invention, the intensity of the radiationbeam emitted by imaging channel 45 is controlled to equal, or exceed anintensity threshold associated with the media. In some exampleembodiments of the invention, the intensity of the radiation beamemitted by imaging channel 45 is varied in relation to a desiredscanning speed.

Controller 60 controls imaging channels such as imaging channel 45 toform image pixels that will result in the formation of desired visiblecharacteristics in image portion 71. In this example embodiment of theinvention, imaging channel 45 is controlled to vary the intensity of itsemitted radiation beam as a function of the scanning direction.Controller 60 can determine the scan direction that is required duringthe formation of image portion 71 in various ways. In one exampleembodiment, imaging head 26 receives a digital real time signal (notshown) named “imaging” and a clock signal which controls the activationtiming of imaging channels 40. Pixel data is received by imaging head 26and is buffered in an internal memory. The imaging signal and the clocksignal determine the specific time for imaging head 26 to form a givenpixel onto the media. The imaging signal activates at the start of theformation of an image swath and remains active for the entire time thatthe image swath is being formed on the media. The imaging signal willthen become inactive until the imaging of the next image swathcommences. In this example embodiment, each activation of the imagingsignal occurs during one of the alternating scan directions. The imagingsignal is thereby used to determine the scan direction during theformation of the various image portions. Those skilled in the relatedart will realize that other methods of determining the scan directioncan be readily used by the present invention.

On completion of the first scan, apparatus 80 is prepared to image asecond image portion 72 during a second scan as shown in step 310. Inthis example embodiment of the invention, second image portion 72includes stripe features 30D. Controller 60 can prepare apparatus 80 forthe second scan in various ways. In this example embodiment of theinvention, imaging head 26 was at a first sub-scan position (i.e.position 38A) while scanning along the scan path related to the firstscan. In this example embodiment of the invention, controller 60 causesmotion system 59 to move imaging head 26 along sub-scan axis 44 to asecond position 38B after the first scan. Imaging head 26 can be movedfrom the first position 38A to the second position 38B in various ways.For example, imaging head 26 can move between the two positions ascarrier 52 decelerates from a speed employed during the first scan,and/or as carrier 52 accelerates to another speed used in a subsequentscan. Carrier 52 can move through a point of zero velocity as imaginghead moves between the two positions. Carrier 52 can pause as imaginghead 26 moves between moving between the two positions. In some exampleembodiments of the invention, imaging head 26 moves from first position38A to second position 38B by a distance that is less than the width ofan image swath. In some example embodiments, second position 38B is thesame as first position 38A (i.e. in a sub-scan direction).

In step 320 imaging head 26 forms second image portion 72 on receiverelement 18. As schematically shown in FIG. 4B, controller 60 controlsimaging head 26 to direct radiation beams in a second scan direction toform second image portion 72 on receiver element 18. The second scandirection is opposite to the first scan direction. During the secondscan, controller 60 controls motion system 59 to move carrier 52 along asecond path. In this example embodiment of the invention, motion system59 to moves carrier 52 with a constant speed as imaging head 26 directsradiation beams to form second image portion 72. Image portions 72 and71 are imaged bidirectionally.

Controller 60 controls imaging channels 40 selected to emit radiationbeams with intensities suitable for forming image portion 72. In thisexample embodiment of the invention, the intensity of the radiationbeams emitted by a given channel while scanning in the second directionis controlled to be different than the intensity of the radiation beamsemitted by the same channel while scanning in the first direction. Forexample, in accordance with image data 240, imaging channel 45 has beenselected to form image pixels during both the first scan and the secondscan. Controller 60 operated imaging channel 45 to emit a radiation beamwith a first intensity while scanning in the first direction during thefirst scan. During the second scan, controller 60 operated imagingchannel 45 to emit a radiation beam with a second intensity whilescanning in the second direction. The second intensity is different formthe first intensity and is selected to enhance, the imaging of secondimage portion 72. The second intensity forms part of set of imagingparameters selected to overcome differences in visual characteristics ofsecond image portion 72 that would occur if it was imaged with the sameimage parameters employed in the imaging of first image portion 71. Insome example embodiments of the invention, the second intensity isselected to produce a different exposure during the imaging of thesecond image portion 72 than the exposure produced during the imaging ofthe first image portion 71. This example embodiment of the invention canbe used to create imaged features that have substantially the samevisual characteristics while benefiting from the productivity gainsassociated with bi-directional scans.

The optimal intensity for the second scan can be determined by a trialand error test. For example, various test pattern images can be formedusing scans at different intensities and examined to determine the bestintensity to minimize differences in visual characteristics.

An example of a measure that can be used to compare an visualcharacteristic of two imaged portions is the value ΔE that representscolor differences in the CIE 1976 L*, a*, b* (“CIELAB”) system asdefined by the Commission International de l'Eclairage (CEE). In someembodiments the differences in intensities are sufficient to achieve ΔEbetween the image portions (e.g. stripe features 30C and 30D) of 3 orless, 2 or less, and preferably 1 or less. In demanding applications ΔEmay be 0.7 or less (e.g. about ½ or less).

Color density is another visual characteristic that can be comparedbetween the imaged portions 71 and 72. Various reflectivity ortransmissivity measures can be compared between the imaged portions 71and 72.

After the formation of image second portion 72, the imaging process canstop as shown in step 330. Alternatively, additional portions of theimage can be formed as per various embodiments of the invention byrepeating steps 300, 310 and 320. Alternatively, additional portions ofthe image can be produced by other techniques.

In some example embodiments of the invention, various portions of theimage can be formed in an interleaved fashion. For example, a firstimage portion can include a plurality of image sub-portions that areseparated from one another in one or more directions. Each of the imagesub-portions are formed by scanning in a first direction during a firstscan. A second image portion can be formed between the separatedsub-portions by scanning in a second direction opposite to the firstdirection during a second scan. A first image portion can be overlappedby a second image portion. Features formed in a second image portion canbe contiguous or non-contiguous with features formed in a first imageportion.

The intensity of radiation beams emitted by each imaging channel 40 canbe varied in a number of different ways. In some example embodiments ofthe invention, imaging head 26 includes a spatial light modulator (lightvalve) that is illuminated by a constant laser source. The laser isdriven by a constant current source adjusted to maintain a desiredoverall power. The light valve is used to attenuate the intensity of theradiation beams emitted from each channel of the light valve to adesired intensity for that channel. For each scan direction, a lightvalve driver switches between two levels for each channel, one for “off”and one for “on”. The level for “on” while scanning in a first directiondiffers from the level for “on” while scanning in a second directionopposite to the first direction. In this example embodiment, the lightvalve works as an analog device that can supply a variable attenuationper channel.

In other example embodiments, the intensity of radiation beams emittedby each imaging channel 40 can be varied by an imaging head 26 whichuses a constant laser source with a pulse width modulated light valve.The laser is driven using a constant current source adjusted to maintaina desired overall power. The light valve is used to attenuate theintensity of the radiation beams emitted from each channel of the lightvalve to a desired intensity for that channel. The level for “on” whilescanning in a first direction differs from the level for “on” whilescanning in a second direction opposite to the first direction. Thelight valve is used in a digital fashion such that a given channel iseither “on” or “off” but the duty cycle is adjusted to control a desiredintensity of the beam emitted from that channel.

In other example embodiments, the intensity of radiation beams emittedby each imaging channel 40 can be varied by an imaging head 26 whichuses a pulse width modulated laser source with a variable attenuationlight valve. The laser is driven using a pulse width modulator where theduty cycle is adjusted to maintain the desired overall power. The lightvalve is used to attenuate the intensity of the radiation beams emittedfrom each channel of the light valve to a desired intensity for thatchannel. The level for “on” while scanning in a first direction differsfrom the level for “on” while scanning in a second direction opposite tothe first direction. In this embodiment, the light valve works as ananalog device that can supply a variable attenuation per channel. Thoseskilled in the art will realize that other methods and imaging headconfigurations can be used to vary the intensity of a radiation beamemitted by an imaging channel. In some embodiments, the imaging headdoes not include a light valve. In some embodiments the imaging channelsare individual laser sources.

FIG. 6 shows a schematic block diagram illustrating a logic used by alight valve driver system 200 as per an example embodiment of theinvention. Light valve driver system 200 is used to operate a lightvalve of an imaging head. Light valve driver 200 system controls theactivation of a number of channels of the light valve. By way of exampleonly, two drivers 200A and 200B are shown and each driver controls acorresponding channel “A” AND “B” of the light valve. Each driverincludes a digital-to-analog converter 204 (DAC 204) to produce ananalog signal proportional to the desired output voltage. A high voltageamplifier 206 (AMP 206) is used to boost the signal to cover the desiredoutput range. For each channel, light valve driver system 200 uses alookup table 208 that stores separate “on values” for each of theopposing scan directions and an “off value”. Each of the on valuescorresponds to a drive signal appropriate to cause a correspondingchannel to emit a radiation beam with an intensity required by that scandirection. On every update clock, selection multiplexer 210 reads a scandirection signal 209 associated with image data 240 and assigns anappropriate “on” value corresponding to that direction. Selectionmultiplexer 212 reads image data 240 to decide whether each channelshould be set to “off” or “on”. In this example, pixel data 240Acorresponds to channel “A” and pixel data 240B corresponds to channel“B”. Depending on the pixel data for that channel (i.e. “on-data” or“off-data” that dictate whether an image pixel is to be formed or not)selection multiplexer 212 selects the “off value” or an “on value”corresponding to scan direction signal 209.

In some example embodiments of the invention, the intensity of aradiation beam emitted by a given imaging channel 40 is adjusted inaccordance with the position of an image pixel formed by that beam inrelation to other formed image pixels. Individual pixels are formed inrelation to one another to produce various portions of an imagedfeature. It may be desired to form various image pixels differently fromone another to enhance imaging. For example, one or more pixelscorresponding to edge portions of a feature may be imaged with radiationbeams that have intensities that are different than the intensities ofradiation beams that are used to image other portions of the feature.“Edge pixels” corresponding to edge portions need not be limited to theperimeter pixels of an imaged feature and can include one or moreadditional pixels that do not directly form the perimeter of thefeature. The additional pixels can include select inboard pixels of theimaged feature. In one example embodiment of the invention,corresponding edge portions of a feature may be imaged with radiationbeams that have higher intensities than the intensities of radiationbeams that are used to image other portions of the feature. The edgeportions can be parallel to one of the first or second scan directions,or can extend in a direction that intersects one of the first or secondscan directions. Increasing the intensity of various radiation beamsused to form edge portions of an imaged feature can be used to enhance avisual characteristic of the features and reduce artifacts such as edgediscontinuities. Edge discontinuities can occur for a number of reasonsincluding for example, differential thermal effects that can arise nearthe transition between imaged and non-imaged areas. In the case ofthermal transfer, mechanical effects, such as insufficient peel strengthassociated with the image-forming material transferred to the edges ofthe features or insufficient control of peel speed, angle or direction,may lead to edge discontinuities when the imaged donor element is peeledaway. Selectively increased intensities can be used to help alleviateimage artifacts such as edge discontinuities. In some exampleembodiments, an imaging channel can form a first pixel and second pixelwith respective radiation beams of differing intensities. Each of thefirst and second pixels is formed while scanning in one of two opposingscan directions. The first and second pixels can be used to form aninterior portion of one or more features formed on a media. The sameimaging channel, or a different imaging channel can be operated to emita radiation beam having an intensity to form a third pixel, wherein thethird pixel is part of an edge portion of one of the one or morefeatures. The intensity of the radiation beam used to form the thirdpixel can be greater than the intensities of the radiation beams used toform the first and second pixels. The third pixel can be formed duringthe same scan that either of the first or second pixel are formed in.

FIG. 7 shows a schematic block diagram illustrating another logic usedby a light valve driver system 220 as per an example embodiment of theinvention. In this example embodiment of the invention, the intensity ofa radiation beam emitted by a given imaging channel 40 is adjusted inaccordance with a scan direction and with the position of an image pixelformed by that beam in relation to other formed image pixels. Like lightvalve driver system 200, light valve driver system 220 includes twodrivers 220A and 220B which include various DACs 204, AMPs 206, andselection multiplexers 210. Light valve river system 220 controls theactivation of a number of channels of a light valve (again, by way ofexample only, two channels “A” and “B” are shown). In this exampleembodiment, each of drivers 220A and 220B uses a lookup table 208 thatstores separate “on values” for each of the scan directions and an “offvalue”. On every update clock, selection multiplexer 210 reads a scandirection signal 209 associated with the read image data 240 and assignsan appropriate “on value” corresponding to that direction. Selectionmultiplexer 212 reads image data 240 to decide whether each channelshould be set with the “off value” or an “on value” corresponding to thescan direction signal.

Each of drivers 220A and 220B also includes edge enhancement circuitry222 (EEC 222) used to determine if image data 240 corresponds toparticular portion of a feature to be imaged. In this example, theportion is an edge portion of the feature. Features such as color filterfeatures are typically formed by a plurality of contiguous image pixels.In this example embodiment of the invention, edge enhancement circuitry222 reviews the pixel data and determines whether a current pixel “n”corresponds to an interior portion of the feature, an edge portion ofthe feature, or an un-imaged area. For example, when considering driver220A, pixel data 240A_(n) is compared against two neighboring pixelsworth of data on either side of it (i.e. 240A_(n−2), 240A_(n−1), and240A_(n+1), 240A_(n+2)). Two pixels worth of data is selected by way ofexample only. In this example, embodiment, the arrangement of pixel data240A_(n−2), 240A_(n−1), 240A_(n), 240A_(n+1), and 240A_(n+2) correspondto a single dimension (i.e. in a scan direction or transverse to thescan direction). The stream of the pixel data can correspond to anarrangement of data that is sequentially fed to a given channel to causethe pixels to be sequentially imaged in the scan direction.Alternatively, the pixel data can correspond to an arrangement of pixeldata that is provided across a group of the channels at a given time. Inthis case, pixel data corresponding to one channel is compared withpixel data corresponding to other channels. In some example embodimentsof the invention, pixel data is analyzed in two dimensions. In thisexample embodiment of the invention, pixel data 240A_(n) is comparedagainst it neighboring pixels and if it is determined that that pixeldata 240A_(n) corresponds to an edge portion of the image feature, thenthe “on-value” is further adjusted to cause a corresponding channel toemit a radiation beam with an increased or boosted intensity level overthe beams used to form interior portions of the feature. Determinationof whether pixel data 240A_(n) corresponds to an edge portion is easilymade by determining which of the other pixel data represent imaged orun-imaged pixel regions. Driver 220B is operated in similar fashion byanalyzing pixel data 240B_(n−2), 240B_(n−1), 240B_(n), 240B_(n+1), and240B_(n+2).

In some example embodiments of the invention, each “on-value”corresponding to a given scan direction is increased by the same amountif the pixel data corresponds to an edge of the feature. In some exampleembodiments of the invention, each of the “on values” is adjusted bydifferent amounts. In some example embodiments of the invention, the “onvalues” are adjusted proportionally. In some example embodiments of theinvention, the “on values” are adjusted to the same value.

In some example embodiments of the invention, an imaging channel 40 isturned “on” to emit a radiation beam having an active intensity levelgreater than an inactive intensity level created when the channel isturned “off”. This active intensity level can be incapable of forming animage pixel on a media. In some example embodiments of the invention,the intensity level of the beam is below an intensity threshold. In someexample embodiments, the intensity of the beam is controlled to createan exposure less than an exposure threshold of the media. Controlling animaging channel to emit a radiation beam with an intensity levelincapable of forming an image pixel is referred to as below-thresholdimaging. Below-threshold imaging can be used to enhance a visualcharacteristic of image features and help reduce some image artifacts.For example, below-threshold imaging can be used to change a thermalcharacteristic in an area at, or near an image pixel to improve aparticular characteristic of that image pixel. In the case oflaser-induced thermal transfer, below-threshold imaging techniques canbe used to promote the adhesion of an image forming material that istransferred from a donor element to receiver element during theformation of an image pixel. In some example embodiments,below-threshold imaging is used to vary the amount of image formingmaterial that is transferred to a given pixel or a neighboring imagepixel to achieve a desired characteristic such as density.

In some example embodiments of the invention, logic circuitry similar tothat shown in FIG. 7 is used to form various radiation beams withbelow-threshold intensities. These radiation beams can be used to scanregions of the media that are represented by “off data” of the pixeldata used to control the turning on and off of corresponding imagingchannels 40. In some example embodiments, these regions are proximatelypositioned to imaged pixels. In some example embodiments, “off-values”corresponding to these regions can be adjusted to cause correspondingchannels to emit a radiation beam with a below threshold intensity. Insome example embodiments, imaged pixels are pre-exposed or post exposedwith radiation beams with below threshold intensities. This belowthreshold exposure can preheat or post heat the media. In some exampleembodiments, the below-threshold intensities can vary as a function ofscan direction.

Imaging head 26 can comprise a multi-channel imaging head havingindividually-addressable imaging channels, each channel capable ofproducing a radiation beam operable form forming an image pixel. Imaginghead 26 can include various arrangements of imaging channels 40including one-dimensional or two-dimensional arrays of imaging channels40. Any suitable mechanism may be used to generate radiation beams. Theradiation beams may be arranged in any suitable way.

Some embodiments of the invention employ infrared lasers. Infrared diodelaser arrays employing 150 μm emitters with total power output of around50 W at a wavelength of 830 nm have been used by the present inventorsin laser induced thermal transfer processes. Alternative lasersincluding visible light lasers may also be used in practicing theinvention. The choice of laser source employed may be motivated by theproperties of the media to be imaged.

Various example embodiments of the invention have been described interms of a laser induced thermal transfer processes in which an imageforming material is transferred to a receiver element. Other exampleembodiments of the invention can be employed with other imagingprocesses and media. Images can be formed on media by differentprocesses without departing from the scope of the present invention. Forexample, media can include an image modifiable surface, wherein aproperty or characteristic of the modifiable surface is changed whenirradiated by a radiation beam to form an image. A radiation beam can beused to ablate a surface of media to form an image. Those skilled in theart will realize that different imaging processes can be readilyemployed.

A program product 67 can be used by controller 60 to perform variousfunctions required by apparatus 80. One such function can includesetting control parameters as a function of scan direction for imaginghead 26 to establish image portions with substantially similar visualcharacteristics as described herein. Without limitation, program product67 may comprise any medium which carries a set of computer-readablesignals comprising instructions which, when executed by a computerprocessor, cause the computer processor to execute a method as describedherein. The program product 67 may be in any of a wide variety of forms.Program product 67 can comprise, for example, physical media such asmagnetic storage media including, floppy diskettes, hard disk drives,optical data storage media including CD ROMs, DVDs, electronic datastorage media including ROMs, flash RAM, or the like. The instructionscan optionally be compressed and/or encrypted on the medium.

In one example embodiment of the invention, program product 67 can beused to configure controller 60 to cause an imaging channel 40 to emit aradiation beam having a first intensity while scanning over receiverelement 18 in a first direction during a first scan, and cause theimaging channel 40 to emit a radiation beam having a second intensitydifferent from the first intensity while scanning in a second directionopposite to the first direction during a second scan. Various imageportions can be formed by the radiation beams during each scan. In thealternative, or additionally, controller 60 may permit manual assignmentor adjustment of the radiation beam intensities under the guidance of anoperator communicating with controller 60 through an appropriate userinterface. Determination of intensity differences can be made on thebasis of suitable algorithms and/or data inputted to controller 60, orprogrammed within program product 67. The control parameters can bedetermined in advance of imaging or may be determined “on the fly” asimaging progresses.

In some example embodiments, controller 60 maintains intensityinformation 224 for each imaging channel 40 that specifies differentintensity values to set for radiation beams emitted by each channel as afunction of scan direction. If it is determined that an imaging channel40 is required to emit a radiation beam while scanning in a determinedscan direction, controller 60 can automatically set the channel to thevalue specified by intensity information 224.

In some example embodiments, controller 60 maintains intensityinformation 224 for each imaging channel 40 that specifies differentintensity values to set for the radiation beams while forming imagepixels while scanning in different scan directions. Controller 60 canmaintain intensity information 224 for each imaging channel 40 thatspecifies different intensity values to set for the radiation beams toexpose the media to different exposures while scanning in different scandirections. Controller 60 can maintain intensity information 224 foreach imaging channel that specifies sets of various intensity values toset for the radiation beams as a function of the direction in which thebeams are scanned. Each of the sets can include one or more intensityvalues that are different from the intensity values of other sets.

In some example embodiments, controller 60 maintains intensityinformation 224 for each imaging channel 40 that specifies a boost inintensity for radiation beam selected to form a particular portion of animaged feature while scanning in a given scan direction. The portion ofthe feature can include an edge portion of the feature. The boostedintensity values are greater than the intensity values of radiationbeams used to form other portions of the feature while scanning in thecorresponding scan direction. Different levels of intensity boost can beset for each of the scan directions.

In some example embodiments, controller 60 maintains intensityinformation 224 for each imaging channel 40 that specifies abelow-threshold intensity to set for radiation beam emitted by animaging channel 40 while scanning in a given scan direction. Differentlevels of below-threshold intensity can be set for each of the scandirections.

Patterns of features have been described in terms of patterns of colorfeatures in a display. In some example embodiments of the invention, thefeatures can be part of an LCD display. In other example embodiments ofthe inventions, the features can be part of an organic light-emittingdiode (OLED) display. OLED displays can include differentconfigurations. For example, in a fashion similar to LCD display,different color features can be formed into a color filter used inconjunction with a white OLED source. Alternatively, different colorillumination sources in the display can be formed with different OLEDmaterials with various embodiments of the invention. In theseembodiments, the OLED based illumination sources themselves control theemission of colored light without necessarily requiring a passive colorfilter. OLED materials can be transferred to suitable media. OLEDmaterials can be transferred to a receiver element with laser-inducedthermal transfer techniques.

Various example embodiments of the invention have been described interms of imaging stripe features. The stripes can have edges extendingparallel to a scan direction. The stripes can be continuous orinterrupted. The invention however is not limited to imaging stripes butcan be used to image features that include other shapes. The inventioncan be used to image island features also.

While the invention has been described using as examples applications indisplay and electronic device fabrication, the methods described hereinare directly applicable to other applications including those used inbiomedical imaging for lab-on-a-chip (LOC) fabrication. LOC devices mayinclude various patterns of features. The invention can have applicationto other technologies, such as medical, printing and electronicfabrication technologies.

It is to be understood that the exemplary embodiments are merelyillustrative of the present invention and that many variations of theabove-described embodiments can be devised by one skilled in the artwithout departing from the scope of the invention.

1. An imaging method comprising: operating an imaging head to emit aplurality of independently-controllable radiation beams while scanningover media to form an image on the media; operating an imaging channelof the imaging head to emit a radiation beam having a first intensitywhile scanning in a first direction over the media during a first scan;and operating the imaging channel to emit a radiation beam having asecond intensity while scanning in a second direction over the mediaduring a second scan, wherein the second direction is opposite to thefirst direction and the second intensity is different from the firstintensity.
 2. A method according to claim 1, comprising forming a firstpixel with the radiation beam having the first intensity during thefirst scan, and forming a second pixel with the radiation beam havingthe second intensity during the second scan.
 3. A method according toclaim 2, comprising forming the first pixel with a first exposure andforming the second pixel with a second exposure, wherein the secondexposure is formed differently from the first exposure.
 4. A methodaccording to claim 2, comprising forming the first pixel with a firstexposure and forming the second pixel with a second exposure wherein thesecond exposure is greater than the first exposure.
 5. A methodaccording to claim 1, wherein each of the first intensity and the secondintensity are sufficient to create an exposure greater than, or equal toan exposure threshold of the media during each of the first scan and thesecond scan.
 6. A method according to claim 1, wherein each of the firstintensity and the second intensity are greater than leakage intensityoccurring when the imaging channel is operated not to emit a radiationbeam.
 7. A method according to claim 1, comprising establishing relativemotion between the imaging head and the media while forming the image.8. A method according to claim 1, comprising selecting the firstintensity to be different from the second intensity.
 9. A methodaccording to claim 1, wherein the imaging head comprises a light valve,the method comprising attenuating a channel of the light valve to makethe second intensity different from the first intensity.
 10. A methodaccording to claim 1, wherein the imaging head comprises a light valve,the method comprising pulse width modulating a channel of the lightvalve to make the second intensity different from the first intensity.11. A method according to claim 1, comprising varying power provided tothe imaging channel to make the second intensity different from thefirst intensity.
 12. A method according to claim 2, wherein the firstpixel forms part of an edge portion of a feature formed on the media andthe second pixel forms part of another edge portion of a feature formedon the media.
 13. A method according to claim 2, wherein the first pixelforms an interior portion of a feature formed on the media and thesecond pixel forms an edge portion of the feature.
 14. A methodaccording to claim 2, wherein the first pixel forms part of an edgeportion of a feature formed on the media and wherein the second pixelforms part of an interior portion of an additional feature formed on themedia.
 15. A method according to claim 2, wherein each of the firstpixel and the second pixel forms part of an edge portion of a featureformed on the media.
 16. A method according to claim 12, wherein atleast one of the edge portions extends in a direction that intersectsthe first direction.
 17. A method according to claim 12, wherein atleast one of the edge portions extends in a direction that is parallelto the first direction.
 18. A method according to claim 2, wherein eachof the first pixel and the second pixel forms part of an interiorportion of one or more features formed on the media, the methodcomprising operating the imaging channel to emit a radiation beam havinga third intensity to form a third pixel, wherein the third pixel is partof an edge portion of one of the one or more features and the thirdintensity is greater than each of the first intensity and the secondintensity.
 19. A method according to claim 18, wherein the third pixelis formed during the first scan.
 20. A method according to claim 18,wherein the edge portion extends in a direction that intersects thefirst direction.
 21. A method according to claim 18, wherein the edgeportion extends in a direction that is parallel to the first direction.22. A method according to claim 1, wherein each of the first intensityand the second intensity is less than an intensity threshold of themedia.
 23. A method according to claim 1, wherein one of the firstintensity and the second intensity is greater than an intensitythreshold of the media.
 24. A method according to claim 1, wherein bothof the first intensity and the second intensity are greater than anintensity threshold of the media.
 25. A method according to claim 2,comprising operating the imaging head to emit a radiation beam having athird intensity, wherein the third intensity is less than an intensitythreshold of the media.
 26. A method according to claim 1, wherein themedia comprises a pattern of registration sub-regions, and the imagecomprises one or more patterns of features, the method comprisingforming the one or more patterns of features in alignment with thepattern of registration sub-regions.
 27. A method according to claim 26,wherein the pattern of registration sub-regions comprises a matrix, andthe one or more patterns of features comprises a pattern of colorfeatures.
 28. A method according to claim 1, wherein the image comprisesone or more patterns of features.
 29. A method according to claim 28,wherein the one or more patterns of features comprises a pattern ofcolor features.
 30. A method according to claim 29, wherein the patternof color features forms a portion of a color filter.
 31. A methodaccording to claim 29, wherein the pattern of color features forms apattern of colored illumination sources.
 32. A method according to claim31, wherein the colored illumination sources comprises an OLED material.33. A method according to claim 28, wherein the one or more patterns offeatures comprises a plurality of patterns of color features, eachpattern of color features corresponding to a given color, the methodcomprising imaging each of the patterns of color features separately.34. A method according to claim 1, comprising forming the image in alaser-induced thermal transfer process.
 35. A method according to claim34, wherein the laser-induced thermal transfer process comprises alaser-induced dye-transfer process.
 36. A method according to claim 34,wherein the laser induced thermal transfer process comprises alaser-induced mass transfer process.
 37. A method according to claim 34,wherein the laser induced thermal transfer process comprisestransferring material from a donor element to a receiver element.
 38. Amethod according to claim 37, wherein the material comprises an OLEDmaterial.
 39. A method according to claim 28, wherein the one or morepatterns of features comprises a pattern of repeating island features.40. A method according to claim 39, wherein the repeating pattern ofisland features comprises a first plurality of features of a firstcolor, each feature of the first plurality separated from each otherfeature of the first color by a feature of a different color.
 41. Animaging method, comprising: operating an imaging channel of an imaginghead to emit a plurality of radiation beams while scanning over media;maintaining intensity information associated with the imaging channel;the intensity information specifying a first intensity to set for aradiation beam in the event that the radiation beam is emitted whilescanning over the media in a first direction, and specifying a secondintensity that is different from the first intensity to set for theradiation beam in the event that the radiation beam is emitted whilescanning over the media in a second direction that is opposite to thefirst direction; determining the direction of a scan; and controllingthe imaging channel according to the intensity information to emit theradiation beam with the intensity corresponding to the determineddirection.
 42. A method according claim 41, wherein the intensityinformation specifies the first intensity in the event that theradiation beam is required to form a first pixel on the media whilescanning in the first direction, and specifies the second intensity inthe event that the radiation beam is required to form a second pixel onthe media while scanning in the second direction, the method comprising:determining if the first pixel is to be formed on the media whilescanning in the first direction; determining if the second pixel is tobe formed on the media while scanning in the second direction; andcontrolling the imaging channel to emit the radiation beam to formeither the first pixel or the second pixel.
 43. A method according toclaim 42, wherein the intensity information specifies the firstintensity in the event that the first pixel is an edge pixel, andspecifies the second intensity in the event that the second pixel is anedge pixel, the method comprising determining if either of the firstpixel and the second pixel are edge pixels.
 44. A method according toclaim 41, comprising controlling the imaging channel to form a firstpixel on the media while scanning in the first direction and controllingthe imaging channel to form a second pixel on the media while scanningin the second direction, wherein the first pixel is formed with a firstexposure and the second pixel is formed with a second exposure differentfrom the first exposure.
 45. A method according to claim 44, wherein thefirst pixel and the second pixel are edge pixels of one or more featuresformed by the imaging head on the media.
 46. A method according to claim44, wherein the first pixel and the second pixel are interior pixels ofone or more features formed by the imaging head on the media.
 47. Amethod according to claim 41, comprising controlling the imaging head toexpose the media with a first exposure while scanning in the firstdirection and to expose the media with a second exposure while scanningin the second direction, wherein the second exposure is different fromthe first exposure.
 48. A method according to claim 41, wherein each ofthe first intensity and the second intensity is sufficient to create anexposure greater than or equal to an exposure threshold of the media.49. A method according to claim 41, wherein each of the first intensityand the second intensity is greater than, or equal to an intensitythreshold of the media.
 50. A method according to claim 41, wherein eachof the first intensity and the second intensity is greater than leakageintensity occurring when the imaging channel is turned off.
 51. Animaging method, comprising: operating an imaging channel of an imaginghead to emit a plurality of radiation beams while scanning over media;maintaining first intensity information associated with the imagingchannel; the first intensity information specifying a first intensity toset for a first radiation beam in the event that the first radiationbeam is scanned over the media in a first direction; maintaining secondintensity information associated with the imaging channel, the secondintensity information specifying a second intensity different from thefirst intensity to set for a second radiation beam in the event that thesecond radiation beam scanned over the media in a second directionopposite to the first direction; determining when the first radiationbeam is scanned in the first direction; setting the intensity of thefirst radiation beam according to the first intensity information;determining when the second radiation beam is scanned in the seconddirection; and setting the intensity of the second radiation beamaccording to the second intensity information.
 52. A program productcarrying a set of computer-readable signals comprising instructionswhich, when executed by a controller, cause the controller to: operatean imaging head to emit a plurality of independently-controllableradiation beams while scanning over media to form an image on the media;operate an imaging channel of the imaging head to emit a radiation beamhaving a first intensity while scanning in a first direction over themedia during a first scan; and operate the imaging channel to emit aradiation beam having a second intensity while scanning in a seconddirection over the media during a second scan, wherein the seconddirection is opposite to the first direction and the second intensity isdifferent from the first intensity.
 53. A program product carrying a setof computer-readable signals comprising instructions which, whenexecuted by a controller, cause the controller to: operate an imagingchannel of an imaging head to emit a plurality of radiation beams whilescanning over media; maintain intensity information associated with theimaging channel; the intensity information specifying a first intensityto set for a radiation beam in the event that the radiation beam isemitted while scanning over the media in a first direction, andspecifying a second intensity that is different from the first intensityto set for the radiation beam in the event that the radiation beam isemitted while scanning over the media in a second direction that isopposite to the first direction; determine the direction of a scan; andcontrol the imaging channel according to the intensity information toemit the radiation beam with the intensity corresponding to thedetermined direction.
 54. An imaging method, comprising: operating animaging head to emit a plurality of independently-controllable radiationbeams while bi-directionally scanning over media to form an image on themedia; while scanning over the media during a first scan, controlling animaging channel of the imaging head to emit a radiation beam having afirst intensity, the first intensity corresponding to an intensity valueselected from a first set of two or more intensity values; and whilescanning over the media during a second scan, controlling the imagingchannel of the imaging head to emit a radiation beam having a secondintensity, the second intensity corresponding to an intensity valueselected from a second set of two or more intensity values; wherein atleast one intensity value of the first set is different from at leastone intensity value of the second set.
 55. A method according to claim54, comprising forming a pixel with at least one of the radiation beamhaving the first intensity and the radiation beam having the secondintensity.
 56. A method according to claim 54, comprising forming aplurality of pixels during the first scan, wherein a first pixel of theplurality of pixels is formed by the radiation beam having the firstintensity and a second pixel of the plurality of pixels is formed byoperating the imaging channel to emit a radiation beam having a thirdintensity, the third intensity corresponding to an additional intensityvalue selected from the first set.
 57. A method according to claim 54,wherein the first set comprises at least one intensity valuecorresponding to a below-threshold intensity.
 58. A method according toclaim 54, wherein each intensity value of the first set corresponds toan intensity sufficient for forming a pixel on the media.
 59. A methodaccording to claim 2, comprising determining if the first pixelcorresponds to an edge portion of a feature formed on the media, themethod further comprising forming the first pixel with a radiation beamhaving a boosted intensity.
 60. A method according to claim 2 wherein atleast one of the radiation beam having the first intensity and theradiation beam having the second intensity is a radiation beam having aboosted intensity.